26th International Microlensing Conference

EROS Microlensing Experiment
Michel SPIRO (International Union of Pure and Applied Physics)

The talk will collect souvenirs and results of the EROS Microlensing Experiment and its relationship with the MACHO Experiment.

The MACHO Project: a historical perspective
Charles Alcock (Center for Astrophysics: Harvard & Smithsonian)

The MACHO Project started in 1989, and started collecting data in 1992. The members of the project team initially comprised people from Lawrence Livermore National Laboratory, UC Berkeley, and the Mount Stromlo & Siding Spring Observatory. The overarching goal was to determine the rate of gravitational microlensing towards the Magellanic Clouds, and use that rate to determine or place upper limits on the contribution of macroscopic objects to the dark matter density in the halo of the Milky Way. This talk will focus on the MACHO Project and its contribution to our understanding of the Milky Way.

Three Decades of the OGLE Survey
Andrzej Udalski (Astronomical Observatory, University of Warsaw)

The OGLE survey pioneered the development of the modern time domain astronomy. For over thirty years it has continuously brought many breakthrough discoveries revolutionizing many fields of modern astronomy. OGLE began regular sky observations in 1992 and it always belonged to the largest photometric sky surveys worldwide. In September 1993 the OGLE project announced the discovery of the first microlensing event toward the Galactic center and during the next three decades it contributed to all major discoveries in the microlensing field. The history and main contribution of the OGLE survey to modern astrophysics will be recalled.

Free-Floating Planets
Takahiro Sumi (Osaka University)

Gravitational microlensing is the only way to find the low mass free-floating planets (FFP) and/or wide orbit planets. The detection of short Einstein radius crossing time microlensing events can be interpreted as evidence for the existence of a population of FFP and/or wide orbit planets. In some short events, the angular Einstein radius are measured. Small angular Einstein radiuses strongly indicate the low mass lenses. We review these previous results and present the Mass Function measurement of FFP from MOA-II 9-year survey.

The Roman Galactic Exoplanet Survey
Scott Gaudi (The Ohio State University)

The Nancy Grace Roman Space Telescope, or Roman, is NASA’s next large astrophysics mission, due to be launched in late 2026 or early 2027. Roman will have a wavelength range, aperture, and angular resolution similar to the Hubble Space Telescope, but will have ~100 times the field-of-view and ~1000 times the sky mapping speed. This means it will be able to map large areas of the sky relatively quickly, or smaller areas of the sky repeatedly with a short cadence. One of the main surveys during the Roman prime mission will be the Roman Galactic Bulge Time Domain Survey (RGBTDS), which will monitor ~2 sq. degrees toward the Galactic center with a cadence of ~15 minutes in a wide 1-2 micron filter over 6 seasons of 62-72 days, for a total survey duration of 372-432 days. One of the primary goals of the RGBTDS is to “Carry out a statistical census of planetary systems in the Galaxy, from the outer habitable zone to free floating planets, including analogs to all of the planets in our Solar System with the mass of Mars or greater.” The component of the GBTDS survey that will achieve this goal is referred to as the Roman Galactic Exoplanet Survey (RGES). NASA recently selected the RGES Project Infrastructure Team (RGES-PIT). The overarching goal RGES-PIT is to ensure that the primary RGES Science Objective is achieved. On behalf of the RGES-PIT, I will summarize the activities of the RGES-PIT over the next five years in support of this goal, focusing on ways in which the larger microlensing, exoplanet, and astronomical communities can get involved.

Observing microlensing events with interferometry
Antoine Mérand (European Southern Observatory)

I will review the recent results of interferometric observations of microlensing events. In particular the ongoing VLTI/GRAVITY upgrade (a.k.a. GRAVITY+) promises to improve greatly the number of targets available. I will show the efforts we have put as a large team in preparing large scale observations and simulating samples with the main objective to detect single black holes. I will also show some possible long term follow up GRAVITY+ can enable.

Towards detection of isolated black holes with ground-based observations
Noam Segev (Weizmann Institute of Science)

The abundance and mass-function of black holes, the last stage of massive star evolution, is fundamental for understanding stellar death and may provide clues regarding the explosion mechanism of core-collapse SNe, and the birth of BH-BH binaries. The study of astrometric microlensing events is currently the most promising path for detecting isolated black holes. However, a measurement of an astrometric microlensing event requires an astrometric precision of 1 mas, and high cadence. We discuss the possibility of detecting astrometric microlensing using seeing-limited ground-based observations. We discuss the limiting factor for ground-based astrometry and describe our efforts to obtain a sub-mas astrometric precision using such observations.

Microlensing in the Era of All-Sky Surveys
Natasha Abrams (University of California, Berkeley)

Gravitational microlensing provides a unique opportunity to probe the mass distribution of stars, black holes, and other objects in the Milky Way. Historically, microlensing events have been discovered primarily in the Galactic bulge by surveys designed solely for that purpose. As we enter the age of visible all-sky surveys, such as that of the Zwicky Transient Facility (ZTF) and Vera C. Rubin Observatory (Rubin), we gain the ability to probe microlensing events throughout the Galaxy. This allows us to analyze galactic structure and how the stellar and black hole mass functions vary across the Galaxy. I will present our analysis of optimal survey strategies, pipelines to discover microlensing events among a billion other lightcurves, and population simulations to physically interpret survey results. For Rubin, we have evaluated 360+ Operation Simulations to find their impact on microlensing discovery and characterization. Microlensing discovery efficiency is dominated by observing footprint, where more time spent looking at regions of high stellar density including the Galactic bulge, Galactic plane, and Magellanic clouds, leads to higher discovery and characterization rates. We also present a multiyear search for microlensing events with ZTF. We discovered 60 high-quality microlensing events in the 3 yrs of ZTF-I using the bulk lightcurves in the ZTF Public Data Release 5. 19 of our events are found outside of the Galactic plane (∣b∣ ≥ 10°), nearly doubling the number of previously discovered events in the stellar halo. To interpret these results we have improved our population simulation tool, PopSyCLE (Population Synthesis for Compact-object Lensing Events) to include binary objects which are typically neglected. Inclusion of binaries in PopSyCLE has brought simulated results into closer agreement with observations from the OGLE survey, and we find that > 50% of our simulated events include a binary lens or source system. Through this work we have shown that open-access, all-sky surveys will be powerful tools for probing galactic structure, exoplanets, and black holes through microlensing.

The Roman IPAC/SSC MSOS Event pipeline: goals, implementation and early results
Etienne Bachelet (Caltech/IPAC)

The Roman Galactic Bulge Time Domain Survey promises to revolutionize our knowledge of exoplanets population by detecting thousands of cold and free-floating planets. The unprecedented data volume that the mission will deliver poses various challenges to extract its scientific content. I will present the goals, the algorithms used as well as early results of the MSOS Event pipeline, developed at IPAC/SSC, in charge of the detection, modeling and characterization of the microlensing events that will be detected by Roman.

Implementation of Automatic Differentiation in Microlensing Light Curve Calculation
Haibin Ren (Tsinghua University)

Analysis of microlensing binary lens events typically demands a protracted duration due to the complexity of the light curve calculation and inefficiency of MCMC’s random walk. To harness the full potential of microlensing technique, we introduce a Jax implementation of the adaptive sampling algorithm with an automatic differentiation function. This implementation enables more efficient optimization algorithms, such as HMC (Hamiltonian Monte Carlo). We demonstrate the utility of gradients by using our package in conjunction with NUTS (No U-Turn Sampler, a variant of HMC) to model several KMTNet events and compare the results with those from MCMC. The integration of gradient information can open new horizons in the machine learning aspect of microlensing analysis.

The public release of RTModel: a platform for the analysis of microlensing events
Valerio Bozza (University of Salerno, Italy)

RTModel has been created in 2010 for the real-time analysis of ongoing microlensing events, with the purpose of making prompt assessments as a service to follow-up observations. An appreciated spin-off of this project has been VBBinaryLensing: a fast and robust public code for microlensing computation. Now we present the public release of RTModel, which is made available to the community along with its specific modules: pre-processing of data; setting of initial conditions for fitting; Levenberg-Marquardt fitting; model selection; final assessment. The success of RTModel is due to three main factors: the exhaustive template library used for initial conditions settings, a filling function strategy to make fitting more effective, and VBBinaryLensing, of course. The main goal of RTModel is to provide preliminary models for a microlensing event in a limited time of the order of two hours. This is useful not only to have up-to-date models for ongoing events, but also to tackle huge data flows, as those expected by Roman. We hope that the publication of the algorithms behind RTModel will be the basis for further developments in microlensing modeling.

Dark microlensing event candidates found in Gaia
Katarzyna Kruszynska (Las Cumbres Observatory)

In 2013, the European Space Agency sent the Gaia satellite towards the L2 point of the Sun-Earth system. Its main scientific goal is to accurately measure the positions and velocities of over one billion stars in the Milky Way. Because it observes the entire Galaxy and takes astrometric measurements with unprecedented precision, it can also be used to search for dark remnants of stellar evolution. This work aimed to find gravitational microlensing events within the data already gathered by Gaia. Events found in Gaia Science Alerts were compiled into a catalogue. Another source of analysed events was the Gaia Data Release~3 microlensing events catalogue, described in Wyrzykowski et al. (2022). For selected events showing a microlensing parallax effect, the best-fitting models were found. If the percentage of light coming from the lens was sufficiently low, we used the obtained solutions to estimate the mass and distance to the lens causing this event. This way we found seventeen candidates for dark remnants.

Gaia22dkvLb: A Microlensing Planet Potentially Accessible to Radial-Velocity Characterization
Zexuan Wu (Peking University)

Microlensing is sensitive to "cold" planets around Einstein radii and provides complementary probes of unexplored parameter space for exoplanets. However, microlensing itself reveals little about orbital dynamics and planet multiplicity, which can be routinely retrieved by Radial-Velocity (RV) techniques. The majority of microlensing planets are discovered in bulge field, where the host stars are typically low-mass stars located far away, thus challenging for RV follow-ups. Here we report the newly discovered microlensing planetary system Gaia22dkv. Our analysis yields a Jovian planet with a turn-off host at r'~14 and it is far brighter than any previously discovered microlensing planet host. With the exceptional brightness and the jovian mass ratio, this system is potentially accessible to large RV facilities, e.g., VLT ESPRESSO, enabling dynamic characterization of the microlensing planet. RV data would also allow for the search of the inner planets of Gaia22dkvLb, as suggested by the "inner-outer correlation" inferred from Kepler and RV discoveries.

Dependence of Planet Frequency on Star Mass and Galactic Distance
Kansuke Nunota (Osaka University)

We examine a dependence of planet frequency on the host star mass, M_L, and distance from the Galactic center, R_L, using a sample of planets discovered by gravitational microlensing. We compare the two-dimensional distribution of the lens-source proper motion, mu_rel, and the Einstein radius crossing time, t_E, measured for the 22 planetary events from Suzuki et al. (2016) with the distribution expected from the Galactic model. Assuming that the planet-hosting probability of a star is proportional to M_{L}^m R_{L}^r, we calculate the likelihood distribution of (m, r). We estimate that r = 0.2 ^{+0.3}_{-0.5}, m = 0.4^{+1.0}_{-0.6}. This result suggests that planets are uniformly distributed in the Galaxy and more massive stars are more likely to possess planets. We also divide the planet sample into subsamples based on their mass ratio and find a possible correlation between the dependence on the host star mass, m, and the mass ratio.

Exploring High-Magnification Microlensing Events from Gaia
Uliana Pylypenko (Astronomical Observatory of the University of Warsaw)

Microlensing events offer a unique opportunity for detecting and measuring the masses of non-luminous objects, particularly in the quest for stellar-mass black holes. Mass measurement through photometry is feasible in specific cases, primarily when the finite source effect is present. This effect is typically observed when the source and lens alignment is nearly perfect, resulting in highly magnified curves. However, within the extensive Gaia Alerts dataset, we have identified high-magnification microlensing events that lack discernible finite source effect. This suggests the presence of a large Einstein radius and, consequently, a substantial mass. Moreover, these events are likely associated with dark lenses. Our analysis has yielded lower mass limits, some of which indicate the possibility that these lenses may be massive enough to be considered strong candidates for neutron stars or black holes. In my presentation, I will introduce these high-magnification microlensing events, characterized by the absence of a finite source effect. I will also discuss the lower mass limits of these lenses, shedding light on their potential identity as stellar-mass black holes.

AMPM: The LMC Asteroid-Mass Primordial black hole Microlensing survey results
Renee Grace Key (Swinburne University of Technology)

A galactic halo population of Primordial black holes (PBH) are a simple solution to the dark matter (DM) problem. Being dark, massive and non-baryonic, the PBH fits within the phenological traits that define Cold Dark Matter, and may exist in large numbers in the dark halos of spiral galaxies. A halo population of PBHs in the Milky Way are best located using microlensing, with several decades of microlensing surveys constraining the vast range of potential PBHs masses and their contribution to halo DM. There remains a single unconstrained mass range of PBH dark matter. High cadence galactic imaging allows the last potential mass range, termed the asteroid-mass range, to be investigated as DM. AMPM is a new survey focused on detecting asteroid-mass PBHs in the Milky Way halo using rapid-fire DECam imaging of 2 million stars in the Large Magellanic Cloud over 5 consecutive nights. Such a vast dataset of stellar light curves also provides novel information into rapidly-evolving transients off-axis from the LMC central, several examples of transient phenomena will be briefly presented in the talk. The focus of this talk will be the survey summary and 95% C.L for a general Milky Way halo model. The most exciting topic of the talk focuses on the presentation of a single, highly compelling low-mass microlensing candidate of estimated mass ~ 10^-7 M\odot detected during the AMPM survey. Discussion will include likelihood analysis of microlensing scenarios (PBH, FFP, etc), as well as parameter modelling of the event.

Status of the PRIME Near-Infrared Microlensing Survey : First year
Naoki Koshimoto (Osaka University)

We report the current status of the near-infrared microlensing exoplanet survey project, the Prime-focus Infrared Microlensing Experiment (PRIME). PRIME observes inner bulge region in H-band and expects a higher event rate than the region observed by the current optical microlensing survey because the stellar density is higher at a lower galactic latitude. In 2022, we built a new 1.8m telescope at Sutherland in South Africa. It mounts an infrared 1.3 deg.^2 field of view camera, PRIME-Cam, which consists of four H4RG-10 detectors. Although only two of the four detectors were in use before June 2023, a service mission was conducted in June 2023 and we started the infrared inner bulge survey with all four detectors in July 2023. This talk summarizes the first year of the PRIME survey including the status of the data processing.

MOA-2010-BLG-328Lb: a Saturn, Neptune or Super-Earth?
Katie Vandorou (NASA Goddard Space Flight Center/ UMD)

Measuring accurate masses of microlensing systems is crucial for the study of exoplanet demographics and formation. There are several ways mass measurements can be made, with one of them utilising high resolution follow-up observations to directly detect the lens star. This method has been in use for several years, with many microlensing events having follow-up data from Keck or HST, and it will be one of the methods used to determine masses following the launch of the Roman Space Telescope. In this talk I will present the Keck and HST data of MOA-2010-BLG-328 – an event with a highly degenerate light curve, where parallax, orbital motion and xallarap all have plausible solutions. Using Keck and HST data we try to unravel the mystery of this planetary event in order to determine its physical properties.

Updates of KMTNet photometry pipeline and systematic reanalysis of history events
Hongjing Yang (Tsinghua University)

We updated the photometry algorithms of the microlensing survey, the Korean Microlensing Telescope Network (KMTNet). The outcome noise is close to the photon Poisson noise. With this more stable and more accurate photometry data, we start a project to systematically reanalyze achieved microlensing events in the KMTNet database. The new data enable the discovery of previously missed anomalies in the light curves with low false positive rates. A statistical sample can be defined with the new data as well. I will present the updates of the photometry pipeline and the discoveries made by the new data.

Gravitational microlensing as a kinematic probe: Rotation curves in five lensed quasars
Carina Fian (University of Valencia)

We study the microlensing response over a range of velocities within the high-ionization lines Si IV and C IV in five gravitationally lensed quasars: SDSS J1001+5027, SDSS J1004+4112, HE 1104-1805, SDSS J1206+4332, and SDSS J1339+1339. We have found a monotonic relationship wherein the microlensing-induced differences increase with velocity, establishing a correlation between the distance from the inner broad-line region (BLR)  to the central supermassive black hole (SMBH) and the emitting region size. We aim to probe the kinematics of the inner part of the BLR by comparing the microlensing responses predicted by a kinematic model to the observed responses across various spectral regions within the broad emission line wings. By deploying a Keplerian model, we assess the consistency of the hypothesis that supports a Keplerian rotation. Overall, our analysis reveals a surprisingly consistent kinematic agreement between the source size estimates derived from microlensing and those obtained from a Keplerian fit. Our effort marks a novel step towards determining the rotational curves of disk-like emitting regions in lensed quasars.

Dark lenses through the dust: microlensing in the near-infrared with the VVV survey
Zofia Kaczmarek (Zentrum für Astronomie der Universität Heidelberg)

Gravitational microlensing is a powerful tool in studies of Galactic populations and structure. However, the most interesting regions — where stellar density is high, lensing events are most frequent, and valuable information about the structure of the central Milky Way regions can be obtained — are obscured by dust and inaccessible to most variability surveys. This limitation can be partially overcome by observing in the near-infrared. We carried out a search for dark lenses in the dataset of 1959 microlensing events found in VVV data by a machine learning classifier. We modelled all lightcurves using the nested sampling algorithm, which allowed for handling multimodal distributions and minimising human intervention in the selection process. We then analysed a selected subset of events in detail using a simple model of the Milky Way, identifying probable dark remnant candidates and giving estimates for their distances and masses. Precision of our estimates is limited by the VVV data quality. To test the possibilities that will be made available within the next decade, we simulated mock data as observed by the upcoming Roman Space Telescope. We demonstrate Roman will provide direct measurement of lens masses to a very high accuracy, without relying on any assumptions about motion in the Galaxy. Finally, we have extended this work to exploit the information obtained from modelling all 1959 events. We analysed the spatial distribution of event timescales and compared it to predictions derived from simulations of the Galaxy, employing hierarchical inference methods. I will present this analysis of microlensing events from the VVV survey. I will also highlight possibilities opened by the use of infrared data in microlensing today and in the near future.

Is it possible to detect effects of wave optics on gravitational lensing?
Arthur Câmara Mesquita (Brazilian Center for Physics Research)

The phenomenon known as femtolenting is generated by the effect of wave optics on gravitational microlensing, producing a frequency-dependent magnification of light that could be detected in the spectra of astronomical objects. Interest in this phenomenon, also known as diffractive gravitational lensing, has led to its application to restrict the abundance of low-mass primordial black holes that would produce femtolensing in the γ-ray frequency range. However, when considering the finite source effect, which destroys femtolensing in cases previously studied in the literature, the limits initially found were discarded. In this work, we expand the study of diffractive lensing by considering a diversity of distance scales, masses and sizes of astrophysical objects (lenses and sources) and taking into account the entire electromagnetic spectrum, aiming to determine whether it is possible to detect this effect with current instruments. To this end, we obtained unprecedented results establishing conditions for detectability of femtolensing in the spectrum of sources lensed by black holes in a wide range of possible masses. If we are able to detect diffractive lensing in the spectrum of an astrophysical source, it would be possible to test for the first time the effect of gravity on wave optics, allowing us to go beyond its use to study the abundance of primordial black holes.

Systematic Planetary Anomaly Search for the 2016 KMTNet archive
In-Gu Shin (Center for Astrophysics | Harvard & Smithsonian)

The KMTNet team is conducting a series of works called "Systematic KMTNet Planetary Anomaly Search" using a semi-machine-based algorithm instead of the conventional by-eye search for planets. The goal of the series is to build a complete microlensing planet sample. As a part of the series, I present the search results for both  high- and low-cadence KMTNet fields observed in 2016. I found nine new planets and eight planet candidates in the 2016 KMTNet archive. I will present these new planetary events that remained undiscovered or unpublished for a long time.

Hunting for Black Holes via Astrometric Microlensing with Keck
Macy Huston (UC Berkeley)

The Milky Way is expected to host nearly 100 million stellar-mass black holes with an unknown binary fraction. One of the only methods for detecting the isolated black holes is through gravitational microlensing. We perform a search for black holes via astrometric follow-up of four long-timescale microlensing events initially detected by OGLE. By combining 10 years of OGLE seeing-limited photometry with diffraction-limited photometric and astrometric monitoring from adaptive optics imagers at the W. M. Keck Observatory, we are able to constrain the masses of the lenses. Preliminary analysis detected significant astrometric microlensing signals in two of the four events and identified one as a probable neutron star or black hole. Here, we present updated results for the four events with improved reduction and analysis techniques for the Keck adaptive optics imaging data, including a non-linearity correction for NIRC2 data and an updated distortion solution for OSIRIS. The sample of black holes found through microlensing will significantly increase in coming years with the addition of Rubin, Roman, and improved astrometry from large, ground-based telescopes equipped with adaptive optics systems.

Measuring mass of OGLE-2012-BLG-563 using High Resolution Imaging
Aparna Bhattacharya (University of Maryland College Park)

My talk will focus on mass measurement of microlensing cold, wide orbit planet using high resolution images, like Hubble Space Telescope and Keck Laser Guide Adaptive Optics imaging. We have observed the event OGLE-2012-BLG-0563 with Keck AO and HST data. I will talk about the analysis of this event with Keck data; the analysis has yielded the smallest separation measured in high resolution imaging for microlensing mass measurements using Keck. This method will also be used to measure mass for upcoming Roman space telescope.

Analyzing Lens Parameter Distribution: A Case Study of the Gaia18ajz Event
Kornel Howil (Astronomical Observatory, University of Warsaw)

Due to its unique nature, microlensing is an ideal technique for detecting and studying dark and compact objects, such as white dwarfs, neutron stars, and black holes. These events can be detected photometrically, as a change in the light curve, or astrometrically, as the shift of the center of light of the source star. Fully analyzing a microlensing event requires both photometric and astrometric data. However, in cases where astrometric data is unavailable, statistical analysis can still provide probability distributions of various parameters, such as the distance and mass of the lens. I will present an analysis of the Gaia18ajz microlensing event, which was detected by the Gaia space telescope. The photometric model was calculated using data from Gaia as well as ground-based telescopes. Since astrometric data for this event is not yet available, a statistical analysis of the parameters of the lens was performed. Using obtained distributions, we propose two possible scenarios for the nature of the lens, where the more exciting one suggests a nearby black hole.  Additionally, I will show the result of a simulation of the Gaia astrometric time series for this event where I try to reproduce the astrometric parameters derived by Gaia with the inclusion of the microlensing effect.

Microlensing Event Modeling for the Roman Galactic Exoplanet Survey
David Bennett (NASA Goddard and the University of Maryland)

The plan for the microlensing analyses of events discovered by in Roman's Galactic Bulge Time Domain Survey (GBTDS) now differs somewhat from the plans considered by the Microlensing Science Investigation Team (MicroSIT). Some of these changes are due to decisions by the Roman Project, but many of them are due to difficulties discovered in the joint analysis of light curve photometry and high angular resolution imaging data that can be the key to determining exoplanet microlens host star masses. I discuss these difficulties and summarize the plans of the newly constituted Roman Galactic Exoplanet Survey Project Infrastructure Team (RGES PIT) to address these problems. I also discuss the three different RGES PIT microlensing modeling efforts.

The Roman IPAC/SSC MSOS Photometry pipeline: framework, goals,  implementation and early results
Sebastiano CALCHI NOVATI (Caltech/IPAC)

The Roman Galactic Bulge Time Domain Survey is expected to revolutionize our knowledge of the exoplanet population by detecting thousands of cold and free-floating planets. At the same time, this will come along with an unprecedented set of Galactic Bulge time domain data which will pose new challenges, and opportunities, for automatic photometry and astrometry light curve extraction. I will discuss algorithms and early results of the MSOS Photometry pipeline being developed at IPAC/SSC to produce the archival data products for this survey.

The ET mission: free-floating planets and beyond
Shude Mao - (Tsinghua University)

I will discuss the Earth Two (ET) mission, in particular the science goals and current status of the microlensing telescope, and its synergy with the KMTNet and Roman.

A code for the computation of microlensing of multiple systems
Vito Saggese (University of Naples Federico II)

The computation of microlensing light-curve is extremely time-consuming. The release of VBBinaryLensing code (based on the contour integration method) has represented a considerable advance in the field, being the fastest public code for the calculation of microlensing effects; however it’s limited to binary events. This work aims to extend and generalise the VBBinarylensing code. We present a new code that can also be applied to analyse systems with more than two lenses; e.g. triple star systems, host star with two planets in the lensing zone or even planetary systems with exomoons. The code implements three different methods: the Singlepoly method, that solves the lens equation by finding the roots of the associated polynomial; the Multipoly, that solves the polynomials re-centered on each lens and the Nopoly, that directly solves the lens equation with a Newton-like approach.  Each of these methods comes with its own set of strengths and weaknesses. The possibility of modelling multiple systems will play an important role in view of new missions. The NASA Nancy Grace Roman Space Telescope, that will be launched in 2026, includes a microlensing planet-finding program and it will be more sensitive than current instruments. Developing a code, which will be made public, that allows to solve systems with several lenses becomes of fundamental importance and would make it possible to contribute decisively to future analyses of microlensing events.

Prediction and systematically search for free-float planets in KMTNet survey
Qiyue Qian (Tsinghua University)

Free-floating planets (FFPs) are expected to be common in our Galaxy. The mass function and number density of the FFP population can provide constraints to the planet formation theories. Microlensing is currently the only method that can detect FFPs in a wide mass and distance range. We use quasi-image level simulation to predict the FFP event rate of the Korean Microlensing Telescope Network (KMTNet) survey, which differs from the current discovered events. To further understand the difference, we are systematically searching for FFPs in KMTNet historical data, which may re-discover missed FFPs, and I will introduce the recent progress.

A New LCOGT Key Project for High-magnification Microlensing Events
Weicheng Zang (Center for Astrophysics | Harvard & Smithsonian)

The mass-ratio function and multiplicity distribution for microlensing planets are still uncertain due to small-number statistics. Follow-up observations of high-magnification (HM) microlensing events can efficiently form a statistical sample, and the LCOGT is the only system that can form a large statistical sample from the follow-up of HM events. Therefore, we proposed and obtained a new three-year LCO key project for follow-up of HM microlensing events, with a total telescope time of ~2200 hrs. With the follow-up from KMTNet and uFUN, the new key project will detect about 50 planets, including about ten low-mass-ratio planets and six multiple-planet systems. Combined with our discoveries during 2020B-2023A, our statistical sample will become three times the Suzuki sample and estimate the mass-ratio function and multiplicity distribution for microlensing planets before Roman's launch.

Microlensing Key Projects at Las Cumbres Observatory: Past, Present and Future
Yiannis Tsapras – (Heidelberg University)

Since its establishment in 2005, the telescope network of the Las Cumbres Observatory (LCO) has been continuously used to monitor microlensing events. Beginning in 2017, several microlensing campaigns have been awarded Key Project status at LCO. These observing programs, steered by a diverse team of scientists from LCO and global partner institutes, have contributed to the discoveries of several exoplanets, as well as Brown Dwarfs and Black Holes. This talk will provide a retrospective look at these campaigns, highlighting some of the discoveries made. I will also discuss ongoing work within our current Key Project and outline our plans for the future.

Initial mass function of the Galactic bulge from binary microlensing events
Raphael Augusto Pereira de Oliveira (University of Warsaw, Astronomical Observatory)

Gravitational microlensing depends primarily on the lens mass and presents a larger occurrence rate in crowded regions, which makes it the best tool to uncover the initial mass function (IMF) of the low-mass stars in the Galactic bulge. The bulge IMF can be obtained from the luminosity function measured by the Hubble Space Telescope if one knows the statistics of binary stellar systems in the bulge. In this sense, we propose to search for and analyze binary-lens/point-source and single-lens/binary-source events in large databases (i.e., OGLE, MOA, KMT), allowing to explore the lower-mass end of the bulge IMF even in unresolved binary systems. We have been implementing a fully-automated approach in the search and characterization of new and previously identified events. With the proper consideration of the detection efficiency, such a large statistics of binaries will provide important constraints for the binary fraction and mass-ratio distribution. In this talk, I will present the methods and current status of this effort, including its performance for a selection of events.

Microlensing's Evolution from Brown Dwarf Dark Matter through an "Extragalactic Planet" to the Roman Space Telescope
David Bennett (NASA Goddard and the University of Maryland)

Paczynski introduced the idea that microlensing could be used to test the idea that brown dwarfs could be comprise for the Milky Way's dark matter, and it sparked the development of the first microlensing surveys because it seemed to be a way to exclude the least popular and least exotic dark matter candidate: brown dwarfs. The first microlensing surveys spurred more theoretical work, including the possibility of detecting exoplanets. I trace the historical development of microlensing from its dark matter origins, to NASA's choice of the space-based exoplanet microlensing survey of the Nancy Grace Roman Space Telescope as its primary method for understanding the demographics of exoplanets in wide orbits.

The Mass-Ratio Distribution from KMTNet
Jennifer Yee (Center for Astrophysics | Harvard & Smithsonian)

On behalf of the Korea Microlensing Telescope Network, I will present our latest results on the planet frequency and measurement of the mass-ratio distribution. Our sample currently includes the nearly 11,500 events from the 2016-2019 seasons, including 110 planets. This is already the largest statistical sample of microlensing events and planets analyzed to date, and work is underway to expand our analysis to include the 2021-2023 seasons.

Massive lenses population from Spitzer and Gaia
Krzysztof Rybicki (Weizmann Institute of Science)

In the quest to explore the Milky Way's population of stellar remnants, we investigate microlensing events observed by the Spitzer Space Telescope between 2014 and 2019. Our focus is on 9 specific events, chosen for their long timescales, small microlensing parallaxes, and joint observations with the Gaia mission, making them promising candidates for massive lenses, that can be also verified through detection of the astrometric microlensing signal. The analysis introduces the methodologies to be applied to the broader Spitzer data set, aimed at constructing the tE-piE diagram and conducting statistical microlensing parallax investigations, which will be useful for  studying the stellar remnants, as well as planetary populations in the Galaxy. The tentative tE-piE plane, which we populate with the 9 selected events, will be presented. Moreover, we identify potential black hole and neutron star candidates, with prospects for confirmation through Gaia's upcoming epoch astrometry in 2025. Our Bayesian analysis, in conjunction with Galactic models and Gaia Data Release 3 proper motion data, unveils a few promising candidates. Some of them are expected to exhibit detectable astrometric microlensing signals in Gaia, offering the possibility of validating their masses.

Gaia space mission and its astrometric capabilities for microlensing
Lukasz Wyrzykowski (Warsaw University Astronomical Observatory)

I will introduce ESA's Gaia space mission which has been operational since mid-2014 and will continue to function until early 2025. I will discuss the intermediate data products that have already been released and the final data release, DR4, that is expected in 2025. I will also explain how Gaia contributes to the field of microlensing through the discovery of ongoing events (Gaia Science Alerts) and through its archival time-series data. Specifically, I will highlight the ability of Gaia to measure astrometric microlensing signal in Gaia's astrometric time-series covering the entire sky down to 21 mag.

Hunting cold planets: Breaking the low mass planet detection limit with Roman and Euclid
Efstathia Natalia Rektsini (University of Tasmania)

The NASA Nancy Grace Roman Space telescope and ESA EUCLID mission have the potential to detect thousands of planets across a broad range of masses and semi-major axes. Meanwhile, a huge increase of exoplanet detections will require fast and rigorous methods to process and exploit the data. One of the limiting factors of microlensing planet searches is to obtain accurate mass measurements. An approach to break this limit is to use constraints from high angular resolution follow-up observations (with KECK and HST) to measure source lens relative proper motions and flux ratios. Bachelet et al. 2022 use simulated EUCLID images of a star field containing 1961 microlensing events that ROMAN will observe. They show that the two joint-surveys will better constrain mass and distance of microlensing events and enable the measurement of planet masses accurately starting from the first year of Roman survey. Here I will present how I treat the same simulated data as in Bachelet et al. 2022 using a new state of the art method to characterize the microlensing events (flux ratio, separation and orientation). Our improved results emphasize the idea that a joint-survey mission will provide a higher number of microlensing events with high precision mass measurements, throughout Roman’s  5-year microlensing survey. Finally, I will explain how this method can also be used for ground-based observations.

Generalized photometric neural network framework
Greg Olmschenk (NASA Goddard Space Flight Center / University of Maryland)

We will present the development of a generalized neural network framework designed to provide astrophysicists with easy access to powerful machine learning techniques. Our work includes a formal evaluation of various common neural network mechanisms as applied to detection, classification, and characterization within photometric data. The framework provides default architectures and training environments which are suitable "off-the-shelf" for many photometric tasks. This framework has been demonstrated on various tasks, including microlensing event detection, planetary transit detection, flare frequency energy estimation, and short period variable identification. The framework is easily adaptable to data from different telescopes, including data at various cadences. For the microlensing community, the framework provides a simple way to apply an established neural network approach to existing or upcoming datasets. While the default configuration functions well for many applications, the framework also provides access to lower-level components if the user requires specialized modification or experimentation. The goal of our framework is to enable astrophysicists to spend more time on researching topics of interest rather than on searching for relevant data.

Some stories from a former EROS PHD student
Jean-Philippe Beaulieu (Institut d'Astrophysique de Paris)

In 1992, I had the opportunity as a PHD student to join a team of mostly particle physicists to search for dark matter via microlensing, the EROS collaboration. One of the very exciting thing for me, was to be observing millions of stars in the Magellanic clouds over several years, with digitalized Schmidt plates and a first 16 CCD camera. We were two PHD students with a total freedom to  actually do “non-dark matter” related stuff, like going after variable stars, Cepheids, RRLyrae, Pre-main-sequence stars, or doing detailed studies of the microlensing events, if one would  ever be detected… because let’s face it at the time, we were also wondering if it was really feasible. So buckle up, let’s travel to 1993-1998,  I will share some stories about EROS, our interactions with MACHO,  the kind of information that you will not find in the science papers…

A precursor Euclid survey of the Roman fields
Jean-Philippe Beaulieu (Institut d'Astrophysique de Paris)

On behalf of the Euclid Science Working Group: In the same way as Kepler satellite has revolutionized the field 10 years ago for hot and warm planets, probing for cold to habitable planets via microlensing is entering its golden age with the NASA Nancy Grace Roman Space Telescope. Over its 450-day survey, Roman will discover around 1400 new planets, including systems similar to ours. Bachelet et al., 2022 have shown that a Euclid survey of the fields to be observed by Roman can give an excellent base for constraining the relative source-lens proper motion of the survey by Roman, which will translate in accurate mass measurement from year-1.  Just after Euclid launch on July 1, 2023, we finalized with ESA the details of implementation of a survey of 4.5 deg2 of Galactic Bulge in VIS, Y, J, H (with 16 dithers), comprising the considered Roman fields due to be done at the end of the Euclid PV phase in October 2023. Because of FGS problem, all the Performance Verification (PV) phase and Early Release Science surveys had been suspended. Discussions for re-scheduling of the observations of the Roman fields are underway now. We will discuss the prospect and power of such survey for a number of science cases, refining the choice of fields to be monitored by Roman using a wider Euclid survey, understanding the structure and extinction on these line of sights, and of course, constraining relative source lens proper motion and mass ratio to obtain accurate mass measurements from year-1 of Roman survey.

Resolving the Very Low Mass Star Hosting the Super-Earth MOA-2007-BLG-192Lb
Sean K Terry (University of Maryland)

I present a joint analysis of high-resolution images from Keck/NIRC2 and HST/WFC3 of the microlensing event MOA-2007-BLG-192. The 11-year baseline between the microlensing event and the Keck observations allows the planetary host star to be detected at a separation of 29.3 +/- 1.2 mas from the background source star. Directly measuring the amplitude and direction of the lens-source relative proper motion allows me to break a critical degeneracy due to incomplete light curve coverage of the planetary anamoly (Bennett+ 2008, Kubas+ 2010). With the lens flux measurement, I use empirical mass-luminosity relations to derive new masses for the host and planet as well as the distance to the lens system.

The pure astrometric microlensing channel: First direct mass of a single white dwarf and prospects for Roman
Peter McGill (Lawrence Livermore National Laboratory)

I will present the analysis of an astrometric microlensing event by a single white dwarf which was predicted using Gaia and followed up with the Hubble Space Telescope. This event permitted the first ever direct gravitational mass determination of a single and isolated white dwarf allowing a test of the white dwarf mass radius relationship. This event happened at wide-impact parameter meaning its signal was purely astrometric. Following on from this I will discuss the prospects for detecting black holes via this pure astrometric microlensing channel with the Roman Space Telescope.

Microlensing Black Hole Shadows
Himanshu Verma (Indian Institute of Technology Bombay, India)

A detailed analysis is presented of the gravitational microlensing by intervening compact objects of the black hole shadows imaged by the Event Horizon Telescope (EHT). We show how the center, size, and shape of the shadow depend on the Einstein angle relative to the true/unlensed shadow size, and how the location of the lens affects the shift, size, and asymmetry of the black hole shadow due to microlensing. Assuming a supermassive black hole (SMBH) casts a circular-shaped true shadow, microlensing can create an asymmetry of up to approximately 8\%, which is twice the asymmetry caused by the SMBH's spin and its tilt relative to us. Furthermore, the size can be enhanced by $\sim$50\% of the true shadow. Currently, the terrestrial baselines of EHT lack the resolution to detect microlensing signatures in the shadows. However, future expansions of EHT including space-based baselines at the Moon and  L$_2$, could potentially enable the detection of microlensing events. For Sgr~A$^*$, an event rate of 0.0014 per year makes the microlensing phenomena difficult to observe even with space-based baselines for the stellar population in the stellar bulge and stellar disk for lens mass $\sim M_\odot$. However, continuously monitoring the shadow of Sgr~A$^*$ could offer novel insights into the compact object population surrounding the galactic center.

Constraints on primordial black holes as constituents of dark matter based on over 20 years of OGLE observations of the Large Magellanic Cloud
Przemek Mróz (Astronomical Observatory, University of Warsaw)

The first microlensing event was discovered almost exactly 30 years ago, following Bohdan Paczyński's idea to search for compact objects in the Milky Way halo with microlensing. Although microlensing survey observations have ruled out compact objects as a dominant component of dark matter, microlensing can be used to search for exotic objects such as intermediate-mass black holes or planetary-mass black holes. Since the timescale of a microlensing event scales as the square root of the lens mass, the timescales of microlensing events due to intermediate-mass black holes are expected to be very long, 1-30 years, rendering their detection difficult. On the other hand, planetary-mass black holes should result in extremely short-timescale microlensing events. Such short-timescale events have been detected toward the Galactic center and are attributed to free-floating planets, but some speculate that they may originate from planetary-mass primordial black holes. The Optical Gravitational Lensing Experiment (OGLE) is one of the longest-running microlensing experiments that has been observing the Magellanic Clouds for over 20 years, enabling one to detect very long-timescale microlensing events that may be due to intermediate-mass black holes. The survey has also recently started a dedicated campaign to search for extremely short-duration events in the direction of the Magellanic Clouds. I will present the results of both projects and discuss constraints on the mass function and frequency of planetary-mass and intermediate-mass black holes that can be inferred from the study of microlensing events detected by OGLE in the past >20 years.

The Roman Galactic Exoplanet Survey: Prospects for Constraining the Frequency of Earth-Analogs
Samson A. Johnson (NASA/JPL)

The Nancy Grace Roman Space Telescope (Roman) will perform its Galactic Bulge Time Domain Survey when it launches in the mid-2020's. Roman will be sensitive to exoplanets with orbital separations from roughly 1 AU to those unbound from any host star with masses as low as ten percent that of Earth's. To improve predictions of Roman's exoplanetary yield, we incorporate the Galactic Model of Koshimoto et al. (2021) into the gulls simulations (Penny et al. 2019). We use this new model to demonstrate Roman's sensitivity to Earth-mass planets in the habitable zone of Sun-like stars. We show the constraints Roman will be able to place on the frequency of such planets by extrapolating from higher mass and wider separation planets.

The epic of EROS: 30 years of research on microlensing and variable stars
Marc Moniez (IN2P3)

EROS, Expérience de Recherche d’Objets Sombres, conducted one of the first systematic temporal surveys in search of gravitational microlensing effects. The initial aim of EROS1 (1990-1994) was the search for massive compact objects in the Galactic halo, using the microlensing effect on LMC stars. But EROS2 (1996-2003) also monitored many other stellar-dense regions in the southern hemisphere, including the SMC and areas less obscured by dust in the plane of the Milky Way. I will also show how quickly most of the consequences of microlensing imagined as early as 1990 have actually been observed, from parallax effects to the most "exotic" caustic-crossing events. I will review the contributions of EROS to the search for microlensing effects, from the first discoveries in 1993 to the most recent results (2022). These latest results were obtained by re-analysing the EROS and MACHO data, whose observation times complement each other. A quick review of the results related to objects of variable luminosity, such as supernovae, Cepheids, RR-Lyrae..., will complete this presentation. I will conclude by commenting on the perspectives of using the EROS archived data in the framework of the LSST survey.

Does source binarity impact the detection efficiency of black holes by microlensing towards the Magellanic Clouds?
Marc Moniez (IN2P3)

Previous estimates of the impact of blending on microlensing detection efficiency towards the Large Magellanic Cloud have not taken into account the possibility of an excess of source pairs separated by a small distance due to binary systems. We have studied the case of these binary sources, which can cause non-trivial events, particularly when the two sources are amplified differently, and established an upper limit to their impact. We first used the Gaia catalog of nearby stars to estimate binarity rates, which we extrapolated to the distance of the LMC. Then, we estimated the maximum fraction of the cases for which a microlensing event could be significantly distorted, as a function of the lens mass. We conclude that a maximum of 6.2% of microlensing events on LMC sources due to halo lenses heavier than 30 solar mass can be affected by the fact that the sources belong to unresolved binary systems. This result was one of the ingredients of the combined analysis of the EROS and MACHO data published in 2022, which ruled out that compact objects up to 1000 solar mass contribute dominantly to the Galactic halo mass. This result also applies to the prospects of searching for microlensing events due to heavy lenses with the Large Survey of Space and Time (LSST) to be conducted at the Rubin observatory.

Disentangling the Black Hole Mass Spectrum with Photometric Microlensing Surveys
Scott E. Perkins (Lawrence Livermore National Laboratory)

Photometric microlensing surveys provide a wealth of information about many topics in astrophysics but are particularly useful for studying populations of black holes, as microlensing is currently the only method capable of observing isolated black holes. Furthermore, the size of photometric microlensing catalogs is continuously growing, allowing for increasingly powerful statistical studies. Unfortunately, the noisy lightcurve data produces wide posteriors on the parameters of individual events, meaning the classification of a lens as a star, black hole, neutron star, etc., is almost never precisely inferable. Current efforts to study populations using photometric microlensing typically relies on making strong assumptions about the lens classification of each event and galactic model, assuming all events in the analysis fall into one category of lens. To improve on these methods, we have pioneered a fully Bayesian methodology that treats the lens classification problem probabilistically, allowing for the formal marginalization over this uncertainty. To validate this methodology, we generated synthetic photometric catalogs reminiscent of OGLE III/IV capabilities that include different populations of primordial black holes, a hypothetical type of black hole with fundamental physics implications. We then assessed our ability to infer the existence of these exotic black hole populations in this controlled environment. In this talk, I will outline this methodology, its effectiveness and the resulting statistical products that it can produce based on this investigation, which includes hierarchical inference about the population models themselves and the classification of individual lenses.

Eighteen Years of Observations with MOA-2
Ian Bond (Massey University)

The second phase of the Microlensing Observations in Astrophysics (MOA-2) survey has been in near continuous operation since 2006. The survey uses the 1.8 m telescope with an 80 Megapixel camera and is amongst the longest operating surveys with the same telescope and camera. As well as microlensing events, these observations have accumulated huge volumes of data on other types of time domain astronomical phenomena. These include transients such as classical novae and dwarf novae as well as regular variable stars and asteroids. In particular MOA has tracked some 200,000 asteroids with 25,000,000 individual photometry measurements with V<21. Here I will review the MOA-2 observational program and assess the potential as an ongoing resource for time domain astronomy.

Finding black holes with microlensing: current and future prospects
Casey Lam (Carnegie Observatories)

Gravitational microlensing is the only practical way of detecting isolated stellar-mass black holes (BHs). Although isolated BHs are expected to constitute the majority of the Galactic BH population, there has only been one confirmed detection to date. Finding and characterizing the isolated BH population is important to understanding a broad range of other astrophysics, from the evolution and death of massive stars, to binary interactions, mergers, and disruptions, to providing context for the population of merging BHs found via gravitational waves. I will discuss the recent detection of an isolated BH, some of the unexpected complications that arose in its analysis, and what we have been able to learn from a sample size of 1. I will then look forward to how we can detect and characterize a population of isolated BHs with future facilities (e.g., the Roman Space Telescope).

Impact of Rubin observations in microlensing events detected by Roman
Aníbal Varela (Universidad de San Martín)

The Nancy Grace Roman Space Telescope (WFIRST) is scheduled to begin its science operations in 2027. It will undertake two main surveys, one of which focuses on exoplanet exploration. By utilizing microlensing, a prominent technique for planet discovery, Roman is expected to make significant discoveries of planetary systems. The exoplanet survey conducted by Roman will specifically target the galactic bulge, covering an area of approximately 2.2 square degrees with high cadence, allowing for a dense coverage of the light curves. In parallel, the Vera Rubin Telescope will start its science operations in 2024, preceding the start of the Roman survey by three years. With its 9.9 square degree field of view and large collecting area, Rubin will image nearly the entire visible sky within a single day, providing light curves for variable objects across the sky. In particular, Rubin will cover the galactic bulge, overlapping with the Roman footprint. The aim of this work is to evaluate the potential enhancement in the discovery rate and the characterization of microlensing events when data from both the Roman and Rubin telescopes are combined. To achieve this, the team conducts simulations of microlensing events generated by planetary systems as observed by both telescopes. Through the fitting of the realistic simulated light curves we are quantifying the improvements in terms of the ability to characterize and detect these planetary systems. This assessment aims to provide valuable insights into the synergy and complementarity of data obtained from Roman and Rubin and may impact the observing strategies of both telescopes. The coordinated operation and analysis of the data from both telescopes will ultimately advance our understanding of exoplanetary systems.

Peering into the Underworld: Characterising microlensing events for kicked compact remnants in a Gaia + GaiaNIR future
David Sweeney (The University of Sydney)

Isolated black holes (BHs) and neutron stars (NSs) are largely electromagnetically invisible. For this reason, our only real prospect of observing these compact remnants is via microlensing, as was done for the first time early 2021. However, characterisation of the microlensing events caused by BHs and NSs is still in its infancy. New N-body simulation are presented which characterises the number and physical characteristics of microlensing events across the entire sky. This is done for the expected yearly microlensing events, to compare to microlensing events identified in Gaia data and to make predictions of the number of microlensing events detectable for the combination of Gaia and GaiaNIR data. These simulations find that every year we can expect 112 BH, 15 NS and 670 stellar microlensing events which cause an astrometric shift larger than 1 mas. Similarly, we can expect 10 BH, 5.8 NS and 2180 stellar microlensing events which cause a photometric magnification larger than 2. These simulations are compared to microlensing event found in Gaia, finding good agreement. Predictions are made for the number of events which will be detectable in the combination of Gaia and GaiaNIR data.

Limits on low-mass Primordial Black Holes beyond M31
Mário de Oliveira Ferreira (Centro Brasileiro de Pesquisas Físicas)

Low-mass Primordial Black Holes (PBH) could produce microlensing events on short time scales. By looking at sources further then the Magellanic Clouds, those scales may be within reach of standard CCDs. Niikura et al. (arXiv:1701.02151) have carried out observations of stars in M31 using HSC at the Subaru telescope. Their result enabled to set up the strongest constraints on the Dark Matter (DM) fraction in the form of PBHs for masses above ~ 10^(-11) Solar masses. This low-mass cutoff is determined by the finite source effects (Niikura et al.; Smyth et al., arXiv:1910.01285; Sugiyama et al., arXiv:1905.06066). At lower masses, wave optics kills the microlensing effect, imposing a hard cutoff at ~10^(-12) Solar mass scales, which is dependent on wavelength (Sugiyama et al.). Here we propose to follow-up galaxies beyond M31, so as to explore the mass range up to the wave optics limit. We discuss which galaxies, instruments and strategies are more suitable to reach this limit and which are the forecasted constraints on the DM fraction in the form of monochromatic PBHs.

Update on the Rubin Observatory: survey strategy, commissioning and early data
Rachel Street (Las Cumbres Observatory)

The Rubin Observatory's Legacy Survey of Space and Time will deliver timeseries photometry of the Southern sky with an unprecedented combination of cadence and limiting magnitude. The survey has the potential to extend the detection of lensing objects to populations in the galaxy that have not previously been explored, particularly Black Holes. As with any complex major project, progress is being made across a number of fronts, all of which ultimately have bearing on its science return, especially in the early phases. Construction of the observatory is nearly finished, though delays in the completion of LSSTCam has lead to revisions in the expected commissioning program and year 1 observations.  The data handling software infrastructure is maturing, together with an ecosystem of tools and platform designed to enable research with these Big Data catalogs. In the meantime, following the latest round of community input into the survey strategy design process, additional simulations have been performed to explore potential synergies with the Roman Mission's survey of the Galactic Bulge. I will give an update on the overall status of the project, discuss the current expectations for the delivery of data products in the early phases of the survey, and highlight opportunities to get involved.

Validating Fisher Matrix Uncertainty Estimates for Roman Galactic Exoplanet Survey Simulations
Farzaneh Zohrabi (Louisiana State University)

The Nancy Grace Roman Space Telescope is set to conduct a comprehensive time-domain survey of the galactic bulge to explore cold exoplanet demographics through gravitational microlensing. However, existing simulations with the gulls code have been more focused on the detection of exoplanets, overlooking their further characterization. To rectify this, we have enhanced the gulls simulation capabilities by incorporating Fisher Matrix (FM) calculations, a valuable tool for estimating uncertainties and correlations between exoplanet and lens parameters. FM enables rapid and computationally efficient uncertainty estimates, making it especially beneficial for complex models such as binary lenses, however it relies on an assumed form of the chi^2 hypersurface that could be wrong. We validate FM-derived estimates by comparing them with Markov Chain Monte Carlo (MCMC) posterior distributions, that can accurately sample from arbitrary posterior distributions but at high computational cost. We present our findings across a range of microlensing scenarios, including single lens events, annual parallax events, free-floating planet events, and bound planet events.  For the latter two categories, we assess Roman’s ability to measure planetary masses in simulated events. By incorporating these methods, we will pave the way to optimize the Roman Galactic Exoplanet Survey on planets that are not just detectable but also characterizable.

SynthPop: A public, modular, python Galactic population synthesis code
Mathew Penny (Louisiana State University)

Population synthesis models of the Milky Way have become an invaluable tool for planning and interpreting data from ever-larger photometric and spectroscopic surveys of the Galaxy. The most popular models provide easy-to-use web interfaces, but lack the ability to easily adjust the model components and/or parameters to either better match data or to quantify the uncertainties of the model's predictions. We present the new SynthPop code, a publicly-available, modular, python implementation of a Galactic population synthesis model. SynthPop is designed to be flexible, enabling the user to prepare or modify Galactic model components through JSON files, to build new components if desired, and to apply modular sequential post processing to enable the modeling of complex survey selection functions or to simulate data analysis. The package also provides an importable python module to enable the user full control over how the model is run. The package is available at on GitHub and can be installed with pip. I will present an overview of the package and a few examples of microlensing use cases.

Exploring the dark side with high-cadence microlensing
William DeRocco (University of California, Santa Cruz)

Microlensing is a powerful technique to observe non-luminous bodies, both within and beyond the Standard Model. In this talk, I will discuss how existing and upcoming microlensing surveys can provide a new window into both planetary formation and the nature of dark matter. I will cover ongoing projects that range from characterizing the Galactic abundance of free-floating planets to searching for primordial black holes and other exotic subpopulations with the Nancy Grace Roman Space Telescope.

Power of many - BHTOM telescope network for time-domain astronomy
Lukasz Wyrzykowski (Warsaw University Astronomical Observatory)

In 2013, within the OPTICON (later OPTICON-RadioNet Pilot) European programme we established a global network of telescopes for long-term time-domain observations. The Black Hole Target and Observation Manager (BHTOM) system has been developed to facilitate this coordination, observation requests as well as automated photometric data processing and modelling. In this presentation, I will show the most recent version of the system and the first scientific results obtained with its help. In particular, I will discuss how BHTOM is utilized for photometric follow-up of microlensing events from Gaia, ZTF, ASASSN, and potentially LSST in the future.

Discovery of free-floating ground and space-based planets through gravitational microlensing
Victor Oyiboka  (Space Generation Advisory Council)

In order to discover exoplanets, a technique known as gravitational microlensing examines the brightness variations of background stars caused by planets' gravitational effects. Future surveys like the LSST may discover a few hundred microlensing events annually in the Small Magellanic Cloud, which could help us detect extragalactic exoplanets. Low-mass planets and brown dwarfs have been discovered through gravitational microlensing at great orbital distances from their stars. Kepler K2 Campaign 9 (K2-2016-BLG-0005Lb) is the first exoplanet discovered through space-based data using gravitational microlensing. It was discovered in 2016. By the end of 2017, 53 exoplanets had been discovered through gravitational microlensing. The first detection of a 4MJ planet at a ∼ 4 au was reported in 2004, and the detection of a 5M planet in 2006. In a two-planet system, the orbital motion during the lensing event was observed in 2008, and the microlens parallax (and lens mass) was calculated in 2015. The discoveries indicate that gravitational microlensing is an effective and independent exoplanet probe over an essential mass and orbital radius range.

A and F spectral type runaway star candidates in the 30 Doradus region of the LMC Using Gaia DR3
Berhe Tewelde Teklhaimanot (University of vale do paraiba)

The relative proper motions of eight A-F type runaway candidate stars, from the eleven cataloged stars by Platais et al. (2018) in the 30 Doradus (30 Dor) region of the Large Magellanic Cloud (LMC), we were investigated using Gaia DR3 data. Three stars, ID 204988, 271782, and  358858 are fast runaways, and two stars, ID 325244 and 373715, are slow runaways in the tangential plane of the 30 Dor region with relative proper motions of μ ≤ 3.92 mas/yr with respect to their neighbors and μ ≤ 4.05 mas/yr with respect to the central cluster R136, which correspond to a tangential velocity of 920.58 km/s and 951.30 km/s, respectively. The remaining three sources, ID 223800, 346142, and 371614, could be unresolved binaries because their astrometric excess noise values are different from zero and need further study to decide. The flight times of the target stars to the young, massive cluster R136 (kinematic ages) are calculated using angular separations from the cluster and their relative proper motions with respect to the cluster. Based on the calculated values of the flight time and relative proper motions, the stars ID 204988, ID 325244, 358858, and 373715 have proper motions and positions consistent with the runaway scenario from R136. The stars ID 204988, 325244, and 373715 have flight times from R136 agreed with ejection from the cluster more or less during the last half of the age of the cluster, whereas the star ID 358858 has flight times from R136 agree with ejection from the cluster during or shortly after the cluster is formed. The origin of the remaining one star, ID 271782, could not be R136 as it has a direction of motion different from the runaway scenario from R136, although its flight time to R136 agreed with ejection from the cluster.

Combining Xallarap and Parallax Effect to Determine the Lens and Source Properties
Zhecheng Hu (Tsinghua University)

The xallarap effect can be used to constrain the Einstein radius. In this talk, I will show that the Spitzer event OGLE-2015-BLG-0845 can be well explained by parallax and xallarap effects, leading to a low-mass M-dwarf lens and binary source with an orbital period of 70 days. I will discuss the detectability of the xallarap effect in general single-lens events and the implication to the search for dark microlenses.

Mass Measurement of a Cold Microlensing Exoplanet using High-Angular Resolution Follow-up Observations
Clément Ranc (Institut d'Astrophysique de Paris)

Microlensing planets sample has been used to derive occurrence rates of planets as a function of the planet-to-host-star mass ratio. The resulting mass-ratio function has then been used to test models of planet formation, resulting in a tension between predictions of the core accretion theory’s runaway gas accretion process and the observations. To strengthen these previous statistical findings on planet occurrence rates, the MOA collaboration is conducting a systematic analysis of the high-cadence MOA-2 survey observations, including more than ten years of observations performed in New Zealand. This systematic analysis led to the discovery of missed exoplanets or unpublished detections. I will present the analysis of one of these events, OGLE-2006-BLG-332/MOA-bin-17, for which high-resolution images have been obtained in 2018 (performed as part of the NASA Key Strategic Mission Support program; PI: Dr. Bennett), and in 2021 using the OSIRIS instrument on a 10m-telescope at the Keck observatory in Hawaii. The planet-to-host mass ratio is ~0.008, but models with higher values are not ruled out from the light curve modeling only. I will show how the joint interpretation of the high-resolution images with the light-curve best-fit models can be used to break microlensing model degeneracies and to measure the actual mass of the host and planet. In particular, the lens can be detected and separated from the source in the 2021 Keck data that strongly constrain the models. The resulting lens system consists of a super giant planet orbiting a 0.4 Solar masses main-sequence star. This analysis is similar to the primary mass-measurement method that the NASA Nancy Grace Roman Galactic Bulge Time Domain Survey will use to detect >1000 planets with masses as low as Mars mass, around G, K, M stars.

Accuracy of measuring microlensing event parameters under no-peak detections.
Makiko Ban (Astronomical Observatory, University of Warsaw)

The lack of peak detection of the microlensing light curve causes the less accurate measurement of the event properties. However, if the light curve epoch ends close to the peak, the disadvantage of missing peak detection is overcome depending on the telescope's sensitivity. These event populations increase the number of confirmed microlensing lens objects at the end. Here, we investigate the accuracy of the event parameter measurements for no-peak light curves. We assumed the sensitivity of the Nancy Grace Roman Telescope (Roman) for our simulations. Even though the peak is not detected, the event has to satisfy the event alerting criteria. Hence, the event is expected to occur in the very beginning or the ending part of the Roman observation period. We test the accuracy of the event parameter measurement along with the time difference between the edge of the observation period and the undetected peak.

The impact of Gaia on microlensing: the cases of Gaia20bof and Gaia21blx
Paolo Rota (Università degli Studi di Salerno)

With the new generation of large-sky surveys we can detect microlensing events across the entire sky. For this purpose the Gaia satellite becomes fundamental. Thanks to its periodical observations that cover our galaxy, more than 350 microlensing events have been detected and more than 1700 predicted. In this work two microlensing events are shown. High cadence follow-up observations were obtained by the OMEGA Project for both events. The first is Gaia20bof, a binary lens system with degenerate models with spectroscopic observations that indicate that the source is located at <2.2 kpc. The second is Gaia21blx, a binary lens system located in the disk where source and blend, that is attributed to the lens, have comparable magnitude. Using the Gaia parallax and considering it as the flux weighted average parallax of lens and source we can get information about the lens system. In addition to this assumption we consider also information obtained from finite source effects and microlensing obtaining a binary system composed by a G star and K star at 2.2 kpc, while the source is a subgiant F star located at 2.4 kpc. These investigations demonstrate the power of microlensing in detecting low-mass binary systems throughout the Galaxy.

Developing Algorithms for Detecting Microlensing Signals in TESS
Atousa Kalantari (Institute for Advanced Studies in Basic Sciences (IASBS))

Microlensing can reveal populations of dim compact objects that are otherwise very hard to find. All-sky surveys depending on their design have the potential to look for these compact objects throughout the sky and help us understand the rate at which these events are expected to happen. the Transiting Exoplanet Survey Satellite (TESS) primarily focuses on finding transiting exoplanets, and we aim at using its comprehensive all-sky survey and high cadence to look for microlensing candidates. We are using traditional detection algorithms used by the community along with innovative machine learning algorithms trained and tested on simulated TESS microlensing light curves and TESS-SPOC Full Frame Image (FFI) light curves. This project is important from various perspectives; the simulations provide an understanding of what we can expect from TESS in microlensing, and our algorithmic approach tested on TESS light curves will provide an opportunity to evaluate various detection methods available to the community and for future all-sky surveys.

Impact of binary orbits on astrometric microlensing signals.
Tanay (Dex) Bhadra (University of California, Berkeley)

When modeling long-duration binary microlensing events, it is important to consider the orbital motion and dynamics of the involved binary system, as the orbital period approaches the duration of the microlensing signal. In previous iterations of the Bayesian Analysis of Gravitational Lensing Events (BAGLE), the orbital motion for binaries was not included. Now, we make corrections for the different proper motions of the primary and secondary sources/lenses involved in the binary system by developing new parameterization classes. These parameterization classes account for linear, accelerated, circular and elliptical orbits. Using these additions to BAGLE, we explore the impact of binary orbits on astrometric microlensing signals.

Database Operations for Efficient Selection of Black Hole Candidates
Anette Brecko (UC Berkeley)

The microlensing alert database (MAD) displays data from several microlensing survey alert systems, from which events that are potentially caused by black holes can be chosen for further analysis and follow-up observation. However, determining potential black hole candidates by eye from a large array of microlensing event data can prove tedious. By editing and streamlining existing software in MAD, we aim to make this database more effective for black hole candidate selection. Additionally, we will incorporate BAGLE (Bayesian Analysis of Gravitational Lensing Events) into the MAD pipeline in order to automate the fitting of microlensing alert data to complex light curve models. This will allow for important factors such as microlensing parallax to be accounted for more efficiently in candidate selection.

Discovery of free-floating ground and space-based planets through gravitational microlensing
Tobi Ajagbe (University of Jos)

In order to discover exoplanets, a technique known as gravitational microlensing examines the brightness variations of background stars caused by planets' gravitational effects. Future surveys like the LSST may discover a few hundred microlensing events annually in the Small Magellanic Cloud, which could help us detect extragalactic exoplanets. Low-mass planets and brown dwarfs have been discovered through gravitational microlensing at great orbital distances from their stars. Kepler K2 Campaign 9 (K2-2016-BLG-0005Lb) is the first exoplanet discovered through space-based data using gravitational microlensing. It was discovered in 2016. By the end of 2017, 53 exoplanets had been discovered through gravitational microlensing. The first detection of a 4MJ planet at a ∼ 4 au was reported in 2004, and the detection of a 5M planet in 2006. In a two-planet system, the orbital motion during the lensing event was observed in 2008, and the microlens parallax (and lens mass) was calculated in 2015. The discoveries indicate that gravitational microlensing is an effective and independent exoplanet probe over an essential mass and orbital radius range.

Follow-up is Still Needed in Breaking Degeneracy — Take KMT-2022-BLG-0440 as an Example
Jiyuan Zhang (Tsinghua University)

Early microlensing planet detections utilize the survey+follow-up mode to solve the contradictory between monitoring a large amount of stars and high-cadence. Then the new-generation high cadence surveys make survey only detection possible. However, we show that nowadays follow-up observation is still needed to break degeneracy. For KMT-2022-BLG-0440, the 2L1S/1L2S degeneracy cannot be distinguished without follow-up data, while the inclusion of follow-up data rules out the 1L2S model and confirms the 2L1S model; and the degeneracy between different 2L1S models cannot be reliably distinguished without follow-up data, while the inclusion of follow-up data rules out the Resonant and Brown Dwarf models and confirms the Central model. We also show that Future Space Microlensing Missions like Roman and Earth 2.0 may need more multi-band observations to break the 2L1S/1L2S degeneracy.

Accelerating Gravitational Microlensing Event Modeling with Machine Learning and GPU Computing
Hunter Harling (University of California Berkeley)

A common method of modeling gravitational microlensing events is through the use of Bayesian analysis software. However, for complex microlensing events, such as those with binary sources and/or binary lenses, searching the parameter space can be incredibly computationally expensive. Furthermore, fitting models with significant amounts of photometric and astrometric data exacerbates this issue. This research aims to accelerate the microlens modeling software BAGLE (Bayesian Analysis of Gravitational Lensing Events) by leveraging machine learning frameworks such as Google's JAX for just-in-time compilation and optimization. In this work, we also explore the applications of GPU computing and parallelized computations to improve BAGLE runtime performance.

Constraining the stellar mass fraction and the quasar accretion disk size of SDSS J1004+4112 with microlensing
Raquel Forés-Toribio (Universitat de València)

The gravitational lens SDSS J1004+4112 is one of the few examples where a background quasar is lensed by a galaxy cluster instead of a single galaxy. With this particular configuration, the light from the quasar images travels mainly through the intracluster medium and the impact of microlensing was expected to be small. However, several observations in the continuum emission and the broad line region detected variability due to microlensing. In this work, we use the 14.5-year monitoring campaign in r-band and the time delays derived from these light curves by Muñoz et al. (2022), to determine the mass fraction that is in form of microlenses at the quasar images positions and the size of the quasar accretion disk size. We compare the histograms of the observed microlensing differences between image pairs with simulated histograms constructed with tracks over magnification maps with the same length as the light curves. The magnification maps have been computed, according to the mass model of Forés-Toribio et al. (2022), for different stellar mass fractions and convolved with different source sizes. Then, the pairs of tracks are selected such that the average magnification difference agrees with the observed ones, in this way, we select the regions of the magnification maps with the proper underlying micro-magnification over the period of observation.

MuSCAT4: a new multiband imager installed to 2m FTS in Australia
Akihiko Fukui (University of Tokyo)

Despise the importance of multiband observations of microlensing events, which can provide not only the color information of the source and lens stars but also the information of dust extinction, there exist few multiband simultaneous cameras in the Southern hemisphere that are available for follow-up observations of microlensing events. We have developed a new four- (g-, r-, i-, and zs-) band simultaneous imager named MuSCAT4, which was successfully installed to the 2m FTS at Siding Spring Observatory in Australia in October 2023. MuSCAT4 is a clone of MuSCAT3, which is mounted on the 2m FTN at Haleakala Observtory in Hawaii. Both MuSCAT3 and MuSCAT4 are operated by Las Cumbres Observatory (LCO) and are open to the LCO community. In this presentation we will describe the specification and performance of MuSCAT4, which is expected to play an important role in following up microlensing events in the Southern sky.

Automatic generation of magnification maps for lensed quasars and supernovae using deep learning
Somayeh Khakpash (Rutgers University)

Better modeling the microlensing variability in light curves of lensed quasars and supernovae enhances accurate measurements of time delays and the Hubble constant along with improving our understanding of quasars structure and the stellar mass distributions in distant galaxies. In the era of Rubin LSST, there will be thousands of events that need microlensing modeling. Traditional modeling approaches use computationally-intensive ray-tracing methods to generate microlensing magnification maps. While libraries of precomputed maps now exist, they only sample the parameter space on a fixed grid, and the data volume is challenging to handle in modeling. An efficient, automated approach will be needed to enhance this process for large volume of data expected from large surveys like LSST. In this project, we have trained an Autoencoder (a type of deep- learning model) on pre-computed magnification maps to reduce their dimension and form a latent space representation while optimizing for acceptable reconstruction of the maps. We then use a Convolutional Neural Network (CNN) to connect the lensing galaxy parameters to the latent space dimension of the maps. Given the trained Autoencoder and the CNN, we then can generate maps for a given set of lensing galaxy parameters in less than a second. This approach will enhance the treatment of microlensing variability in analysis of light curves for lensed quasars and supernovae.

Analysis of Planetary Events with Pronounced Anomalies in OGLE Survey Data
Mateusz Mróz Warsaw University Astronomical Observatory)

Statistical studies of planetary systems are essential for enhancing our understanding of their formation and evolution processes. The need for accurate occurrence rates of planetary systems in microlensing events necessitates the use of uniform survey data. In this context, as a step in calculating planetary occurrence rates within the OGLE survey, I conducted an analysis of OGLE observations of two microlensing events featuring planetary anomalies: OGLE-2014-BLG-0221 and OGLE-2015-BLG-1609. For both of these events, OGLE data alone provide a consistent coverage of light curves, making them ideal case studies. Notably, OGLE-2015-BLG-1609 is a rare case where data from a single telescope could not be adequately fitted with a 2L1S parallax model, leading to considerations of a 2L2S model and the possibility of a xallarap effect. In my presentation, I will provide a comprehensive analysis of both events, employing the fitted models.

CLEoPATRA: Contemporaneous LEnsing Parallax and Automated TRansient Assay
Richard K. Barry (NASA)

CLEoPATRA is a space mission concept in support of the Roman Space Telescope science mission. CLEoPATRA, a 50 cm telescope in Earth orbit, will capitalize on Roman's exquisite photometric precision and spatial resolution to obtain mass estimates for bound and free-floating bodies detected by the mission. CLEoPATRA would launch into orbit as a SMEX mission in 2031 in support of Roman's extended mission.

Convolutional Neural Networks for Microlensing Detection within Photometric Light Curves
Stela Ishitani Silva (NASA Goddard Space Flight Center)

Wide-field telescope surveys, like the one conducted by the Microlensing Observations in Astrophysics (MOA) collaboration, consistently monitor millions of celestial objects, accumulating extensive datasets over the years. While mining this vast volume of data to identify microlensing exoplanetary signatures already poses challenges, an even greater hurdle awaits. The Nancy Grace Roman Space Telescope promises to collect hundreds of millions of precise light curves, an even greater data influx. Neural networks have emerged as potent tools to address this challenge. In this presentation, we propose using convolutional neural networks to facilitate gravitational microlensing detection. Our ongoing project uses the nine-year MOA dataset, containing 2.4 million light curves, of which 23 thousand received human-inspected labels. Our strategy uses only raw photometric light curves as input for our neural network pipeline, which, after training, can detect microlensing signals in the light curve in milliseconds. This approach aims to provide an alternative pipeline to accelerate the identification of potential microlensing exoplanets.

How to derive planet occurrence rate using microlensing events with degenerate solutions?
Radosław Poleski (Astronomical Observatory, University of Warsaw)

Interpretation of microlensing light curves often approaches degeneracies. Some of these degeneracies are severe (i.e., the model light curves differ very little) and involve significantly different physical interpretations. The presence of such degeneracies hampers the derivation of statistical properties of lensing objects, most importantly occurrence rate. I will discuss how the hierarchical Bayesian approach can be used to account for degenerate microlensing models in calculations of the planet occurrence rate. In particular, I will present how this approach can be used to re-analyze Suzuki et al. (2016) planet occurrence rate. The presented approach can be used in the future analysis of the Roman Space Telescope microlensing planet sample.

The Good, the Bad, and the Ugly: Microlensing in Tasmania and OGLE-2015-BLG-1395Lb
Andrew Cole (University of Tasmania)

Tasmanian observers have contributed to microlensing exoplanet searches since the late 1990s. The opening of the Greenhill Observatory, named in honour of the late Dr John Greenhill, began a new era for astronomy at the University of Tasmania in 2013. The bespoke Harlingten 1.27m telescope was immediately put to work observing the Galactic bulge before commissioning had even finished, observing the extremely high-magnification binary lens event OGLE-2015-BLG-1395. At roughly the same time, a major flaw in the primary mirror was identified, triggering a long process of review, replacement, and ultimately refiguring. Subsequent adaptive optics follow-up on OB15-1395 has allowed us to characterise the lens as a cold, Saturn-mass planet in orbit around an early M dwarf in the Galactic disk. The system makes an interesting test of the ability to determine event parameters with Spitzer parallaxes.  In 2022 the commissioning of a Planewave 50cm telescope has added to our ability to track high magnification events with flexible scheduling. With excellent image quality, this telescope has been our main instrument as we finalise the fixes to the H127 mirror, now expected to be complete in the third quarter of 2024. Moving along with the trends in the field toward the support of space-based microlensing, we have recently received funding to acquire a near-infrared Teledyne InGaAs camera that will allow us to observe out to H-band from the improved H127 telescope from 2024 and beyond.

PBHs and the Origin of the CMB
George Chapline (Lawrence Livermore National Laboratory)

In order to explain the abundance of galactic seeds the initial population of PBHs must be formed at a finite cosmological redshift. Observation of this endpoint for the PBH spectrum using microlensing plus astrometric shifts could explain the entropy of the universe (# CMB photons per gram of DM).

Tuning microLIA for Rubin LSST microlensing light curve identification
Karen Nowogrodzki (Universidad Nacional de San Martín / ICAS / ICIFI)

With its unprecedented combination of area, depth and cadence, the Vera Rubin Legacy Survey of Space and Time (LSST) will open new frontiers for discovering transient events, including microlensing. Given that LSST will produce about 10 million transient alerts per night, it is crucial to have systems, known as brokers, that aggregate and combine the data, generate light-curves and attempt to classify the events. In this context, it will be imperative to have good methods for the real-time classification of those light-curves in the many classes of transients, to enable follow-up observations. In particular, early detection and follow-up observations of microlensing events are essential due to the need for higher cadence sampling than what LSST will provide. In this work we discuss the use of the machine learning-based MicroLensing Identification Algorithm (MicroLIA, Godines et al.) for light-curve classification in LSST simulated data. We use data from the Extended LSST Astronomical Time-Series Classification Challenge (ELAsTiCC) and our own simulated light curves to train and fine-tune MicroLIA. In particular, we test different selections of the training data and filter selection to achieve the best results in terms of microlensing classification. We will also discuss progresses in incorporating MicroLIA into the FINK broker and in reproducing our optimization procedure for the Zwicky Transient Facility (ZTF) data.

A fast approximation for the magnification of point lenses and circular sources of arbitrary size
José Pereira da Silva Neto (Federal University of Pernambuco (UFPE))

The Nancy Grace Roman Space Telescope, as well as other new infrastructures, is expected to lead to the discovery of thousands of free-floating planets (FFP) through microlensing. The proper identification and fitting  of the corresponding light-curves will require extremely fast and accurate methods to compute the magnification of point lenses for finite size sources. In this work we present a very simple approximation for the Uniform Source Point Lens (USPL) case for arbitrary source sizes. We compare the accuracy and computational time of our method to the direct calculations of the Elliptical integrals involved (Witt & Mao, 1994) and also with the methods available from the public packages MulensModel and pyLIMA. We find that our approximation is accurate to about ~1% in the relevant source size - impact parameter space and is much faster that the other methods. In most cases, the light-curve parameters are recovered with good accuracy using our approximation.

CuRIOS: Gravitational Microlensing with the CubeSats for Rapid Infrared and Optical Surveys (CuRIOS)
Hannah Gulick (University of California, Berkeley)

The rise of time-domain astronomy including electromagnetic counterparts to gravitational waves, transient phenomena, and even astrometry with Gaia, are showing the power and need for surveys with high-cadence, large area, and long time baselines to study the transient universe. CuRIOS (CubeSats for Rapid Infrared and Optical Surveys) will be a constellation of 16U CubeSats that will study star death and afterlife by providing all-sky, all-the-time observations at ~15 minute cadence. The initial CuRIOS payload design is optimized to detect microlensing signatures in the Galactic Center, LMC, and SMC with a roughly 7 deg by 5 deg wide field-of-view and high spatial resolution of ~2.5” across the field. With the full constellation of several hundred CubeSats, transients at any point in the sky will be observed down 21st magnitude in 15 minute integrated exposures with an SNR = 10. We present the general design for the CuRIOS payload and report on the expected science returnables for gravitational microlensing as determined through simulations using the Population Synthesis for Compact-object Lensing Events (PopSyCLE) code.

MutliNest sampling in the BAGLE Model Fitter and its performance based in the number of live points sampled
Abby Schleigh (University of California, Berkeley)

BAGLE (Bayesian Analysis of Gravitational Lensing Events) is a tool for the modeling and fitting of gravitational microlensing events, especially those of long duration such as black hole events. BAGLE simultaneously treats both photometric and astrometric data for microlensing models, including PSPL (point-source, point-lens), BSPL (binary-point-source, point-lens), and PSBL (point-source, binary-point-lens), all with or without parallax. We ran performance tests of run time and accuracy based on the number of live points used to fit simulated events with MultiNest (a nested-sampling alternative to MCMC). Running these performance tests allows us to optimize the accuracy and efficiency of BAGLE model fitting. These results were used in determining the optimal number of live points when introducing BAGLE to a new audience through a tutorial.